When performing various types of inspection and measurement by rotating a workpiece, such as a bearing ring, a so-called “centering” operation which makes a center of the workpiece coincide with a rotational shaft of a rotational measurement table is required. Particularly, in the case of large and heavy workpieces, frictional force between the measurement table and the workpiece becomes large, and the workpiece will deform even if it is pressed to correct its position. Therefore, there are difficulties in centering.
Conventionally, the workpiece auto-centering apparatus disclosed in Patent Document 1 includes a rotational reference table, a movable table placed on the reference table for fixing the workpiece, fixed switching means for switching the movable table relative to the reference table between a fixed state and a non-fixed state by hydraulic pressure, floating means for floating the movable table from the reference table by fluid pressure, a measuring apparatus for measuring a misalignment direction and a misalignment amount of the workpiece fixed on the movable table, and a horizontal moving mechanism for moving the workpiece in a horizontal direction together with the movable table. The workpiece auto-centering apparatus performs centering by moving the workpiece based on the misalignment direction and the misalignment amount of the workpiece measured by the measuring apparatus.
Moreover, there has been known a workpiece auto-centering apparatus including a plate which is rotatable around a reference axis and on which the workpiece is placed, a measuring device for measuring a misalignment direction and a misalignment amount of the workpiece, a pusher for moving the plate by pushing the same, and centering means for making an axis of the workpiece coincide with the reference axis by controlling the rotation of the plate and the pusher according to the measurement result of the measuring device (for example, see Patent Document 2).